Reports on the Philadelphia International Exhibition of 1876.

Date:: 1877-1878

Credit: Reports on the Philadelphia International Exhibition of 1876. Source: Wellcome Collection.

375/446 page 277

$Besides affording this security it serves also to transport the caisson or dome from place to place, and is a working platform from which the drilling engines are operated. The caisson or dome is a hemisphere of the diameter of .30 feet, Caisson or dome composed of a strong iron frame covered with boiler iron. The dome is open at bottom and at top, and is provided at the bottom with legs to support and level it, which are arranged to let go altogether after the dome is lowered. The hemispherical shape of the caisson is favourable to stability. The Details, caisson or dome is simply a framework affording a fixed support to 21 drill tubes, through which the drills operate. The dome is connected with the scow by four chains communicating with four hoisting engines, by which it is lowered or raised. A framework is built upon the scow around the well-hole to support the carriage holding the drill engines, which by these means may be' placed directly over the drill tubes. The engines simply raise the drill rods, and allow them to fall hy their weight upon the rock, the vertical play being 18 inches ; the drill and drill rods together are about 10 feet long, and weigh from 600 to 700 lbs. The cutting edges are in the form of a cross, and are 5^ inches long. The scow having the dome swung by chains is first anchored over the rock Method of to be operated upon, so that the bow and aft moorings pull against the direct emPloying it- currents of the ebb and flood tides, but as these may vary somewhat in direction from one tide to another, as well as during the course of the same tide, it^ becomes necessary, in order to steady the scow, to have side anchors also. The diver descends to ascertain whether the location is well suited to placing the dome on the bottom, and if not, td select a better. The required change in the position of the scow is made by lengthening and shortening the mooring chains with capstans, which are arranged to be worked at will with steam or man power. The dome is then lowered, and when it touches or approaches near the bottom the legs are let go, and being held by self-acting cams support the weight of the dome. The chains are now unslung from the dome, which is thereby without connection with the scow. The diver descends to ascertain which of the drill tubes it is necessary to use to break up the rock within the dome, and how the surface offers itself to each particular drill. The drill rods being introduced within the drill tubes, which is easily effected during the most violent currents, a rope or other flexible connection is now made between the top of the drill rod and the piston rod of the drilling engines. A flexible connection is necessary to the act of drilling, as in this machine, the dome remaining fixed upon the bottom in one position, while the scow holding the drill engines swings for short distances from changes in the directions and strength of the currents, no rigid connection between the engine and drills would be practicable. The length of the rope attachment is regulated by a feed-gear for the rise and fall of the tides and continual changes of water-level. The drilling being completed, preparations are made for charging the holes Blasting with nitro-glycerine. The chains are hooked on the dome, which is then operations, raised from the bottom, and the scow swung off from the spot to a safe distance without casting loose the moorings. This distance will depend upon the proposed amount of clmrge of nitro-glycerine, and will' vary from 1/5 to doU ieet. Ihe nitro-glycerme, in tin cases of different lengths, to suit the varying depths of the drill-holes, is carried to the spot upon a small scow, from which the diver descends to the first hole to be charged. He is guided to this by a line ^ ithdramng the plug, he introduces into the hole the tin cartridge, which has been filled by the men on the scow and passed down to him. Lach cartridge is attached before it is sent down to the wires The cW hen passes on to the second hole, guided by the plug-line which con- nects the stoppers of the adjacent holes, and in this way the whole circuit of btrv\vT' tl !?harge( • !ThC lea<?inS Wires ar* connec^ with the To yh al the+fnia11 sc™ haS be,en withdrawn, and the explosion is made. feeT JS„fU?h ^0V0U^Y the drill-holes should be from 6 to 8 ieet apart, of the size of 5^ inches at the top, and charged with amounts ra/^Vlf r^ff hA W Average brt^^and 60 ^SS£ for each, and the depth to which the drill-hole should reach below the evel to which it was desired to break the rock is about four feet I™* broke\by *he explosion covers the greater part of the reef its removal is commenced. This is effected by means of a steam grapple! s 2$

Reports on the Philadelphia International Exhibition of 1876.

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